Method of making readily disintegrating projectile cores for practice ammunition



3,216,358 r; PROJECTILE N 1965 G. FINDEISEN METHOD OF MAKING READILY DISINTEGRATIN CORES FOR PRACTICE AMMUNITI Filed July 22, 1963 //7:/e/7/0/ Ger/20rd F/nde/sen By /7/s af/om eys United States This invention relates to a method of making readily disintegrating projectile cores for practice ammunition, from metal powder, more particularly iron power, which is compressed to produce compacts forming the projectile cores.

The loading mechanism of modern semi-automatic and fully automatic weapons is actuated by the recoil impulse which occurs when the shot is fired or by the gas pressure or both, and is determined largely by the accurately defined projectile weight, since the impulse consists of the product obtained when the mass of the projectile is multiplied by the muzzle velocity. During practice firing, in which ammunition without ballistic effect is required, as is known, the firearm must pass through the same work ing cycle as in the case of firing live rounds, that is to say the explosion of the fired cartridge, the ejection of the cartridge case, the self-loading process and the recoil impulse must be the same as in firing live rounds. It must also be possible to mix live and blank ammunition in the magazine or in the belt without any deleterious effect on the loading mechanism of the weapon.

In order to fulfill this requirement, when known practice ammunition with projectile cores made of wood or the like is used structural modifications of the weapon are required, which increase the recoil. It is also known to use practice ammunition which has projectile cores consisting of compacts made by powder metallurgical methods. These compacts are pressed with a degree of compression such that their strength is adequate to withstand transportation and handling. The projectile cores are usually made up of a plurality of compacts which are held together by a thin rigid sleeve made for instance of plastic material. The sleeve is completely filled by the compact; in some cases a small space is provided for accommodating a drying tablet in order to prevent corrosion of the compacts. The sleeve has exactly the same external dimensions as a live projectile. The green strength of the compacts must be so low that on leaving the bore of the weapon the projectile will be reduced to fine powder by the gas pressure and the rotation produced by the rifiing. The projectile cores of practice ammunition for modern high-speed weapons have to have a relatively high specific gravity. But metal powder compacts which have this necessary specific gravity cannot be made, by the methods known hitherto, with sufficiently low strength to ensure the required disintegration after firing. The reasons for this are that the green strength, that is to say the strength of the pressed products which have not been subjected to sintering, is essentially dependent on the space-filling or the porosity of the pressed product. The green strength and the space-filling are closely related to one another. Each of these properties determines the other, and they are directly proportional to one another; the depending relationship between them is of parabolic form, and usually can only be ascertained empirically. Therefore, if the practice projectile has to have a high specific gravity, then the compact used for this purpose becomes too strong when compressed, and on leaving the bore is not reduced to powder but only breaks up into fragments having a shrapnel effect. High specific gravity 3,216,358 Patented Nov. 9, 1965 calls for a large applied pressure in the making of the projectiles, and this large applied pressure produces a high green strength.

These disadvantages are removed by the present invention. The invention includes the step of subjecting compacts previously fabricated by known powder metallurgical processes such as compression to a subsequent and distinct treatment which weakens their internal cohesion so that their green strength is reduced without destruction of their external shape. Therefore, the metal powder compacts are first made without regard to their green strength, and care is taken only to ensure that they have the required high specific gravity. In this state the projectiles cannot be used, because their strength is still very great. But when the green strength is reduced in accordance with the invention, a projectile core is obtained which is reduced to fine powder upon leaving the bore.

In accordance with further features of the invention the internal cohesion of the compacts can be weakened either by pressing, impact, hammering or similar mechanical action. The compacts may also be subjected to the action of ultrasonic vibrations or alternating magnetic fields for this purpose. The mechanical treatment of the compacts may take place in a mould. The compacts forming the projectile core may also be treated in a sleeve which forms part of the finished projectile.

The following experiment is described by way of further explanation.

If a ram of a press is made to exert pressure on a compact of cylindrical shape, a pressure measuring device provided on the press shows that the pressure rises with time, similarly to the force in the case of a tensile test with a tensile testing machine. At first the pressure rises rapidly and uniformly, and then the rate of increase becomes less. A slight drop follows, and the pressure then drops abruptly. The compact then disintegrates. If the applied pressure is made to cease when the pressure stops rising it is then found, surprisingly, that the test piece shows no external signs of the effect of the pressure, but that the green strength of the test piece has been very greatly reduced. The specific gravity and dimensions of the test piece remain unchanged.

According to a further feature of the invention the internal cohesion of the compacts can also be weakened by the action of chemical substances, for instance acids. For instance, if the compact is immersed in a mineral acid after having been compressed, this acid acts on the areas of contact of the powder grains, which areas have been subjected to a considerable degree of cold working. Be cause of the large extent to which they have been deformed these contact areas are points at which the acid will act readily, and therefore the cohesion of the powder grains, which largely determines the green strength of the compact, is destroyed while the external shape of the compact remains unchanged.

This effect can be made greater if the compact already contains chemical compounds which react with the permeating acid. This is the case more especially if the compact contains sodium carbonate. When a compact of this kind is immersed in hydrochloric acid, not only does the acid act on the metal grains but also carbon dioxide is formed in the capillary passages of the compact by the reaction of the sodium carbonate with the hydrochloric acid, and escapes and thereby weakens the inner cohesion of the compact.

Examples of the use of the method of the invention are particularly described hereunder.

Example 1 In order to make a two-centimetre projectile with a prescribed specific gravity of 6.50 grammes per cubic centimetre, a mixture of an atomized iron powder with 1% by weight of magnesium oxide and 1% by weight of zinc stearate is first made, and is compressed under an applied pressure of 6.5 tons per square centimetre to form compacts. The green strength of these compacts is then 1.5 kilogrammes per square millimetre and their density is 6.57 grammes per cubic centimetre. After compression, the compacts are subjected to a static pressure of 3.3 tons per square centimetre. The green strength is then only 0.07 kilogramme per square millimetre. The external shape of the compacts remains unchanged.

The abovementioned value for green strength is so low that projectile cores made from these compacts are reduced to fine powder when fired.

Example 2 For two-centimetre projectiles with a prescribed density of 7.20 grammes per cubic centimetre, a mixture of an atomized iron powder (RZ powder) having a grain size of about 600 microns with 1% of zinc stearate was compressed under an applied pressure of 12 tons per square centimetre to form compacts of which the green strength was then 1.8 kilogrammes per square millimetre. After the products had been subjected to a static pressure of 3.5 tons per square centimetre their green strength was only 0.09 kilogramme per square millimetre. These pressed products also were pulverised when fired.

The drawing shows a projectile for practice ammunition. Three compacts 2, 3 and 4 made by the method of the present invention form the projectile core and are arranged in a sleeve 1 of plastic material which has the external shape of the projectile. A drying tablet 5 made of calcium chloride is accommodated in the tip of the projectile core and prevents corrosion of the projectile core during storage.

Iclaim:

1. A method of making readily disintegrating projectile cores for practice ammunition comprising the known step of compressing iron powder in a die to form compacts,

in combination with the steps of removing each compact from the forming die,

thereafter applying increasing mechanical force against each compact to cause pressure within the same to rise, thus weakening the green strength without changing the external shape of the compact,

and removing the increasing mechanical force from each compact when the internal pressure stops rising.

2. A method of making readily disintegrated projectile cores according to claim 1 including between the steps of removal from the forming die and application of increasing mechanical force, the step of placing each compact in a container, such as a second die, which surrounds the compact.

3. A method of making readily disintegrated projectile cores for practice ammunition comprising the steps of compressing iron powder to form compacts and subjecting said compacts to alternating magnetic fields to weaken the internal cohesion of said compacts and to re duce their green strength.

Jones, 1960, Edward Arnold (Publishers) Ltd., London,

The Physics of Powder Metallurgy, W. E. Kingston, 1951, McGraW-Hill, New York, pp. 360-366.

Treatise on Powder Metallurgy, C. G. Goetzel, 1949,. Interscience Publishers Inc., New York, pp. 119, 120.

BENJAMIN A. BORCHELT, Primary Examiner. 

1. A METHOD OF MAKING READILY DISINTEGRATING PROJECTILE CORES FOR PRACTICE AMMUNITION COMPRISING THE KNOWN STEP OF COMPRESSING IRON POWDER IN A DIE TO FORM COMPACTS, IN COMBINATION WITH THE STEPS OF REMOVING EACH COMPACT FROM THE FORMING DIE, THEREAFTER APPLYING INCREASING MECHANICAL FORCE AGAINST EACH COMPACT TO CAUSE PRESSURE WITHIN THE SAME TO RISE, THUS WEAKENING THE GREEN STRENGTH WITHOUT CHANGING THE EXTERNAL SHAPE OF THE COMPACT, AND REMOVING THE INCREASING MECHANICAL FORCE FROM EACH COMPACT WHEN THE INTERNAL PRESSURE STOPS RISING. 